Endoscopic and laparoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. The use of laparoscopic and endoscopic surgical procedures has been relatively popular and has provided additional incentive to develop the procedures further. In laparoscopic procedures, surgery is performed in the interior of the abdomen through a small incision. Similarly, in endoscopic procedures, surgery is performed in any hollow viscus of the body through narrow endoscopic tubes inserted through small entrance wounds in the skin.
Laparoscopic and endoscopic procedures generally require that the surgical region be insufflated. Accordingly, any instrumentation inserted into the body must be sealed to ensure that gases do not enter or exit the body through the incision. Moreover, laparoscopic and endoscopic procedures often require the surgeon to act on organs, tissues and/or vessels far removed from the incision. Thus, instruments used in such procedures are typically long and narrow while being functionally controllable from a proximal end of the instrument.
Significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.).
Known surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
An example of a surgical stapler suitable for endoscopic applications is described in U.S. Pat. Appl. Pub. No. US 2004/0232196 A1, the disclosure of which is hereby incorporated by reference in its entirety. The disclosed surgical stapling and severing instrument enables a clinician to close the jaw members upon tissue to position the tissue prior to firing. Once the clinician has determined that the jaw members are properly gripping tissue, the clinician can then fire the surgical stapler to sever and staple the tissue. The simultaneous severing and stapling avoids complications that may arise when performing such actions sequentially with different surgical tools that respectively only sever or staple. In addition, a retraction spring assists in retracting firing components so that the jaws may be unclamped to release the stapled and severed tissue portions.
Thus, while such surgical staplers have provided a significant advancement in surgical procedures, further features would be desirable, such as reducing the force to fire. The requirement of a higher force to operate the trigger may be inconvenient or difficult for a surgeon with limited hand strength. One successful approach to lowering the force to fire is utilizing multiple firing strokes, as described in U.S. patent application Ser. No. 11/052,632, entitled “MULTI-STROKE MECHANISM WITH AUTOMATED END OF STROKE RETRACTION”, to Swayze et al., filed 7 Feb. 2005, the disclosure of which is hereby incorporated by reference in its entirety. However, it may be desirable in some instances to retain the simplicity of a single firing stroke, or to reduce force to fire during each stroke of multiple firing strokes.
Consequently, a significant need exists for an improved surgical stapling and severing instrument that effectively severs and staples tissue, but with a reduced amount of force required to pull a firing trigger to cause the severing and stapling.